Sphingosine-1-phosphate (S1P) has been demonstrated to induce many cellular effects, including those that result in platelet aggregation, cell proliferation, cell morphology, tumor cell invasion, endothelial cell and leukocyte chemotaxis, endothelial cell in vitro angiogenesis, and lymphocyte trafficking. S1P receptors are therefore good targets for a wide variety of therapeutic applications such as tumor growth inhibition, vascular disease, and autoimmune diseases. S1P signals cells in part via a set of G protein-coupled receptors named S1P1 or S1P1, S1P2 or S1P2, S1P3 or S1P3, S1P4 or S1P4, and S1P5 or SIPS (formerly called EDG-1, EDG-5, EDG-3, EDG-6, and EDG-8, respectively).
S1P is important in the entire human body as it is also a major regulator of the vascular and immune systems. In the vascular system, S1P regulates angiogenesis, vascular stability, and permeability. In the immune system, S1P is recognized as a major regulator of trafficking of T- and B-cells. S1P interaction with its receptor S1P1 is needed for the egress of immune cells from the lymphoid organs (such as thymus and lymph nodes) into the lymphatic vessels. Therefore, modulation of S1P receptors was shown to be critical for immunomodulation, and S1P receptor modulators are novel immunosuppressive agents.
The S1P1 receptor is expressed in a number of tissues. It is the predominant family member expressed on lymphocytes and plays an important role in lymphocyte trafficking. Downregulation of the S1P1 receptor disrupts lymphocyte migration and homing to various tissues. This results in sequestration of the lymphocytes in lymph organs thereby decreasing the number of circulating lymphocytes that are capable of migration to the affected tissues. Thus, development of an S1P1 receptor agent that suppresses lymphocyte migration to the target sites associated with autoimmune and aberrant inflammatory processes could be efficacious in a number of autoimmune and inflammatory disease states.
Among the five S1P receptors, S1P1 has a widespread distribution and is highly abundant on endothelial cells where it works in concert with S1P3 to regulate cell migration, differentiation, and barrier function. Inhibition of lymphocyte recirculation by non-selective S1P receptor modulation produces clinical immunosuppression preventing transplant rejection, but such modulation also results in transient bradycardia. Studies have shown that S1P1 activity is significantly correlated with depletion of circulating lymphocytes. In contrast, S1P3 receptor agonism is not required for efficacy. Instead, S1P3 activity plays a significant role in the observed acute toxicity of nonselective S1P receptor agonists, resulting in the undesirable cardiovascular effects, such as bradycardia and hypertension. (See, e.g., Hale et al., Bioorg. Med. Chem. Lett., 14:3501 (2004); Sanna et al., J. Biol. Chem., 279:13839 (2004); Anliker et al., J. Biol. Chem., 279:20555 (2004); Mandala et al., J. Pharmacol. Exp. Ther., 309:758 (2004).)
An example of an S1P1 agonist is FTY720. This immunosuppressive compound FTY720 (JPI 1080026-A) has been shown to reduce circulating lymphocytes in animals and humans, and to have disease modulating activity in animal models of organ rejection and immune disorders. The use of FTY720 in humans has been effective in reducing the rate of organ rejection in human renal transplantation and increasing the remission rates in relapsing remitting multiple sclerosis (see Brinkman et al., J. Biol. Chem., 277:21453 (2002); Mandala et al., Science, 296:346 (2002); Fujino et al., J. Pharmacol. Exp. Ther., 305:45658 (2003); Brinkman et al., Am. J. Transplant., 4:1019 (2004); Webb et al., J. Neuroimmunol., 153:108 (2004); Morris et al., Eur. J. Immunol., 35:3570 (2005); Chiba, Pharmacology & Therapeutics, 108:308 (2005); Kahan et al., Transplantation, 76:1079 (2003); and Kappos et al., N. Engl. J. Med., 335:1124 (2006)). Subsequent to its discovery, it has been established that FTY720 is a prodrug, which is phosphorylated in vivo by sphingosine kinases to a more biologically active agent that has agonist activity at the S1P1, S1P3, S1P4, and S1P5 receptors. It is this activity on the S1P family of receptors that is largely responsible for the pharmacological effects of FTY720 in animals and humans.
Clinical studies have demonstrated that treatment with FTY720 results in bradycardia in the first 24 hours of treatment (Kappos et al., N. Engl. J. Med., 335:1124 (2006)). The observed bradycardia is commonly thought to be due to agonism at the S1P3 receptor. This conclusion is based on a number of cell based and animal experiments. These include the use of S1P3 knockout animals which, unlike wild type mice, do not demonstrate bradycardia following FTY720 administration and the use of S1P1 selective compounds. (Hale et al., Bioorg. Med. Chem. Lett., 14:3501 (2004); Sanna et al., J. Biol. Chem., 279:13839 (2004); and Koyrakh et al., Am. J. Transplant., 5:529 (2005)).
The following applications have described compounds as S1P1 agonists: WO 03/061567 (U.S. Patent Publication No. 2005/0070506), WO 03/062248 (U.S. Pat. No. 7,351,725), WO 03/062252 (U.S. Pat. No. 7,479,504), WO 03/073986 (U.S. Pat. No. 7,309,721), WO 03/105771, WO 05/058848, WO 05/000833, WO 05/082089 (U.S. Patent Publication No. 2007/0203100), WO 06/047195, WO 06/100633, WO 06/115188, WO 06/131336, WO 2007/024922, WO 07/109,330, WO 07/116,866, WO 08/023,783 (U.S. Patent Publication No. 2008/0200535), WO 08/029,370, WO 08/114,157, WO 08/074,820, WO 09/043,889, WO 09/057,079, and U.S. Pat. No. 6,069,143. Also see Hale et al., J. Med. Chem., 47:6662 (2004).
There still remains a need for compounds useful as S1P1 agonists and yet having selectivity over S1P3.
Applicants have found potent compounds that have activity as S1P1 agonists. Further, applicants have found compounds that have activity as S1P1 agonists and are selective over S1P3. These compounds are provided to be useful as pharmaceuticals with desirable stability, bioavailability, therapeutic index, and toxicity values that are important to their drugability.